1. Field of the Invention
The present invention relates to a system and method for wireless resource allocation, and a base station used therefor, and more specifically, to a wireless resource allocation scheme in a system for performing high speed uplink packet transfer.
2. Description of the Prior Art
In a system using an EUDCH (Enhanced Uplink Dedicated Channel), which is a high speed uplink packet transfer scheme for WCDMA (Wideband Code Division Multiple Access), a base station performs scheduling, and a mobile station performs packet transfer on an uplink based on the scheduling.
A mobile station in the system using EUDCH transmits a DPCCH (Dedicated Physical Control Channel), an E-DPCCH (Enhanced-Dedicated Physical Control Channel) and an E-DPDDH (Enhanced-Dedicated Physical Data Channel) on an uplink. A closed loop-type control is performed on the transmission power of the DPCCH at the base station so as to satisfy predetermined reception quality.
Transmission power of E-DPDCH for data transfer performs transmission at a power obtained by adding a predetermined power offset to the transmission power of the DPCCH. The higher the transfer rate, the higher the power offset must be. In addition, transmission power of the E-DPCCH for control is basically a power obtained by adding a predetermined power offset to the transmission power of DPCCH.
In order to maintain communication at a predetermined quality, the base station must control total reception power so that the total reception power, or the ratio of total reception power to thermal noise (noise rise) is equal to or lower than a predetermined threshold. Therefore, the base station will perform scheduling on a mobile station so that the total reception power or noise rise will be equal to or lower than a predetermined threshold to control an available power offset SG (Serving Grant) that represents a wireless resource or, in other words, a power resource of a mobile station.
In addition, during E-DPDCH transmission, a mobile station is capable of notifying a buffer size representing data size to be transmitted, and a Power Headroom representing wireless communication quality, as scheduling information (for instance, refer to 3GPP TR25.321 V6.5.0 (2005-06) “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Medium Access Control (MAC) protocol specification (Release 6)”, p. 48). A base station determines power resources to be allocated using scheduling information. Power Headroom represents power obtained by subtracting DPCCH transmission power from a maximum transmission power of a mobile station. Since the higher the Power Headroom, the greater the power allocatable to E-DPDCH, a high transfer rate may now be selected.
On the other hand, a mobile station selects a transmission format of a transport block to be transmitted at a unit transmission time (TTI: Transport Time Interval) on a physical layer from a usable power offset range. The transmission format of a transport block is referred to as an E_TFC (Enhanced Transport Format Combination). An E_TFC table is comprised of an E_TFC index corresponding to a power offset, and a transport block size (TBS) or the like.
Furthermore, 3GPP (3rd Generation Partnership Project) is presently evaluating an EUTRA (Evolved UTRA [Universal Terrestrial Radio Access]) system, which is an expansion of the WCDMA system. In regards of the EUTRA system, discussions are ongoing mainly over SC-FDMA (Single Carrier-Frequency Division Multiple Access) as an uplink wireless access scheme (for instance, refer to 3GPP TR25.814 V1.0.1 (2005-11) 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical Layer Aspects for Evolved UTRA (Release7)”, p. 41), wherein transmitting bands will be allocated as wireless resources. It is conceivable that, in an uplink of an EUTRA system, the base station will determine wireless resources to be allocated using scheduling information of the size of data to be transmitted and the like, in the same manner as in the case of EUDCH.
However, the above-described wireless resource allocation method according to EUDCH has the following problem. The problem existing in the wireless resource allocation method will now be described with reference to FIG. 8. FIG. 8 shows timings at which a base station allocates wireless resources, timings at which a mobile station “a” transmits data, and a time series of buffer size at the mobile station “a”.
In FIG. 8, the processing time from allocation of a power resource by the base station to transmission by the mobile station “a” based on the allocated power resource is assumed to be 4 TTIs. For instance, a power resource allocated at time 2nd TTI by the base station may be used by the mobile station “a” from time 6-th TTI. It is additionally assumed that, upon an initial occurrence of transmission data, the mobile station “a” is capable of performing one transmission using a predetermined transport block regardless of presence of an allocated power resource (at time 2nd TTI). Furthermore, the mobile station “a” transmits scheduling information during data transmission by EUDCH.
At this point, as shown in FIG. 8, when allocation of a power resource of the mobile station “a” is performed using a buffer size notified from the mobile station “a”, a power resource allocated at time 8 to 10-th TTI will be nullified since the buffer size is 0 at time 12 to 14-th TTI, which is the time of transmission. At this point, utilization efficiency of the power resource may be improved if the power resource is allocated to a mobile station other than the mobile station “a” under the base station. Useless allocation of a power resource occurs because the report time of the buffer size of the mobile station “a” differs from the time of transmission using the power resource allocated based on the buffer size.
This problem is not unique to WCDMA systems, and may occur in any system in which a base station performs scheduling of a mobile station in a wireless mobile communication system, due to the difference between the time at which a scheduler allocates a wireless resource and the time at which a mobile station actually performs transmission using the allocated resource.
Therefore, since a report time of a buffer size of a mobile station and a time at which a wireless resource determined based on the buffer size similarly differ in an EUTRA system using SC-FDMA, a problem arises in that a wireless resource or, in other words, a transmission band is uselessly allocated. In this case, since SC-FDMA does not allow a plurality of users to be allocated to the same transmission band, when a wireless resource is uselessly allocated, no mobile station will be able to transmit data using the transmission band during such allocation.
Therefore, an object of the present invention is to solve the above-described problem, and to provide a wireless resource allocation system and method thereof, and a base station used therein, which are capable of avoiding useless allocation of wireless resources and improving utilization efficiency of wireless resources.